Conventionally, a variety of reciprocating linear drive means have been provided for large, automated clinical analyzers. Generally, these involve pushers or pullers that engage a test element for movement along a generally horizontal support surface, called a "track", from underneath or above, that support surface. Examples are shown in U.S. Pat. Nos. 4,152,390, issued May 1, 1979; and 4,219,529, issued Aug. 26, 1980.
Although generally effective for their intended use, such mechanisms are generally large and expensive. Furthermore, they have other disadvantages: a claw mechanism that protrudes upwardly from underneath can upset a test element if the claw projections are not accurately aligned with the element's edges. A claw protruding downwardly from above does not have this disadvantage, but it does tend to occupy the space within the track. As a result, access to the track, such as to clear a test element jam, is difficult to obtain. This has not been a serious difficulty in large analyzers serviced by highly skilled personnel. However, in a simpler machine located in a doctor's office, the users are generally not skilled enough for such disassembly. Thus, when smaller analyzers were designed for the doctor's office, in the interest of simplicity, the linear advancing mechanisms have been a simple pusher blade that is either manually operated, or directly driven by a simple motor connection. Examples of both appear in, e.g., U.S. Pat. No. 4,424,191. Such simple blades, although effective, lack a positive engagement with the test element--that is, there are no provisions for positively gripping the test element. For this reason, the advancing mechanisms of such smaller analyzers lack the ability within the pusher blade itself to control the sideways location of test elements on the generally horizontal support surface.
What has been desired prior to this invention is an advancing mechanism that is not as cumbersome as those used in the larger analyzers, but which provides positive sideways control of the test element within the portion that contacts the element for movement.